Aircraft wings are provided with airfoils or so-called high lift systems which extend from the wing edges. The high lift devices are known as “stats” (when on the wing leading edge) or “flaps” (when on the wing trailing edge).
Actuating mechanisms cause the flaps or slats to lift or lower relative to the wing to vary aerodynamic drag or lift. This allows the aircraft to be accelerated/decelerated for better control on take off and landing.
Conventionally, the flaps/slats are driven by two separate actuators—one on each end of the flap/slat. These are coordinated to lift/extend the flap or slat in a uniform manner. If one of the actuators fails or does not operate properly, the panel can be skewed or asymmetrical relative to the wing. This can adversely affect the control of the aircraft.
It is important, therefore, to be able to detect and report/respond to such skew in high lift devices. Indeed, it is now a requirement that aircraft include skew detection systems.
Various mechanical and electrical/electronic skew monitoring systems have been discussed. Current mechanical solutions consist of routing a cable along the length of the wing through each moving panel, such that panel skew would displace the cable to signal a switch. Alternatively, lost motion devices are sometimes used to detect a change in the structural load path due to mechanical failure. Both cable based and lost motion based solutions provide significant installation challenges and monitoring accuracy can be poor.
Current electrical/electronic solutions consist of individual sensors mounted at each panel linkage point, the outputs of which are typically connected to a central processing point and are compared against each other to identify abnormal position information. Sensor based solutions require significant aircraft level wiring since all sensors come to a single point, add significant interface complexity to the central computer (a typical flap system would require 16 RVDT interfaces to monitor 4 panels), and require the integration of complex monitoring software into the flap/slats electronic control units. U.S. Pat. No. 5,680,124, US 2010/0100355 and U.S. Pat. No. 8,646,346 all describe skew detecting systems using electrical/electronic sensors.
It is desirable to provide a skew monitoring system that is less complex and less prone to failure.